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Development and Processing of Dielectric Films for Application in Large Wound Capacitors
Navy SBIR 2012.1 - Topic N121-095 ONR - Ms. Tracy Frost - tracy.frost1@navy.mil Opens: December 12, 2011 - Closes: January 11, 2012 N121-095 TITLE: Development and Processing of Dielectric Films for Application in Large Wound Capacitors TECHNOLOGY AREAS: Ground/Sea Vehicles, Materials/Processes, Weapons ACQUISITION PROGRAM: Rail Gun INP, Roger Ellis, ONR 352 OBJECTIVE: Develop and process a dielectric film that: has increased energy storage density relative to very thin Biaxially-Oriented PolyPropylene (BOPP); has low dielectric and leakage losses in a wound capacitor; exhibits graceful failure; and retains performance to 125C or higher. DESCRIPTION: For electrical systems that require significant capacitative energy storage, polymer film capacitors, such as BOPP, are often used because the technology is scalable and they can exhibit graceful failure. BOPP is a state-of-the-art polymer dielectric film in that it has high dielectric breakdown strength, very low dielectric loss, can exhibit graceful failure when appropriately metalized, and can be processed into thin, large area films with uniform dielectric performance and minimal flaws. The weaknesses of BOPP are however, the low permittivity which limits energy storage density and a rather low maximum temperature for sustained use. Commercial polymer dielectric films with higher operational temperature capability typically have lower energy storage density and/or show less ability for graceful failure. In academic laboratories, many approaches are being taken towards dielectric films with increased energy storage capability (i.e., Polyvinylidene Fluoride (PVDF) terpolymer, nanocomposites and nano-layered approaches (see References)). There is, however, a large hurdle in going from laboratory films prepared by spin casting or thermal pressing to films prepared by commercially viable approaches such as extrusion or reel-to-reel casting. Commercial approaches to thin films offer the possibility of improving dielectric performance by improving film quality across large areas (flaw reduction) and by providing a means for altering film morphology through annealing and orientation. However, the capability to study and pursue dielectric film development and optimization through processing does not exist in many academic laboratories. There is a need for increased energy density and a higher thermal performance window relative to capacitors produced from the most common dielectric film currently used for larger capacitors. These improvements will allow smaller electrical components on ships and will allow components to operate without dedicated cooling systems. PHASE I: Offerers must develop a dielectric film that outperforms BOPP on lab-prepared films and demonstrate that they can retain 80% of the energy storage density with a first step towards a commercial process such as using a laboratory extruder, doctor blading a large area, etc. At the end of Phase I, both lab-prepared films and scaled films must be presented to the Navy for testing as follows: - At least 10 square inches of film (multiple pieces accepted) prepared in the lab and at least 40 square inches of continuous film prepared through processing that demonstrates scalability. The offeror will be able to submit a reasonable number of films to the Navy for testing during Phase I and expect results in a reasonable time (less than 2 weeks). PHASE II: The goals of Phase II are to fully develop an optimum dielectric film processed on commercial or near commercial* equipment and to demonstrate performance both on the film level and in wound capacitors. Work may include synthesis scale-up, process development runs on commercial or near commercial equipment, studies of the influence of processing variables on film morphology and dielectric properties, etc. There should be a milestone near the midpoint of this effort to finalize film work and begin work towards the wound capacitor deliverable. At this point, film samples will again be supplied to the Navy. Based on the characteristics of the optimized film, metrics for the wound capacitors will be agreed upon. Typical metrics might be for delivering several 10 joule capacitors with a 1 kHz discharge time, graceful failure, desired temperature performance, and a wound capacitor energy density above 2 J/cc. *Near commercial equipment has capability and features such that the width of the film (amount of raw materials required) and the speed of the machine are the only major operating differences relative to commercial equipment. PHASE III: The goal of Phase III is to deliver a number of fully packaged capacitors for potential use in a military component. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Capacitors are part of all electrical components. The focus in this solicitation is for increased energy density and a higher thermal performance window relative to capacitors produced from the most common dielectric film currently used for larger (applications besides microelectronics) capacitors. If successful, the dielectric film will likely compete against established capacitors made using BOPP, especially where volume is critical or when the electronics are housed in a hot environment. REFERENCES: 2. "Phosphonic Acid-Modified Barium Titanate Polymer Nanocomposites with High Permittivity and Dielectric Strength," P. Kim, et al, Adv. Mater. 2007, 19, 1001-1005. 3. "Enhanced Breakdown Strength of Multilayered Films Fabricated by Forced Assembly Microlayer Coextrusion" M. Mackey, et al. J. Phys. D: Appl Phys. (2009) 42, 175304. KEYWORDS: wound capacitor; dielectric film; metalized film; graceful failure; polymer; processing
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